1. Field of the Invention
This invention relates to improvements in a radioactive matter containing waste gas treating installation and more particularly to improved apparatuses for treating waste gas containing radioactive matter which is produced in the case of incinerating combustible radioactive waste delivered from atomic energy installations such, for example, as an atomic energy research laboratory, atomic power plant, nuclear fuel treating installation, nuclear fuel reprocessing work and radioactive isotope treating installation and the like.
2. Description of the Prior Art
Recent increase of atomic energy installations results in that the amount of radioactive waste is increased and hence large and many storage houses are required. In addition, it is not desirous to store the radioactive waste as it was just delivered from the atomic energy installations for the sake of safety.
As a result, the combustible radioactive waste is incinerated so as to considerably reduce its volume and ashes remained are solidified with the aid of cement or asphalt so as to make these ashes chemically stable. Such treating method is optimum from both econimical and safe standpoints. For this purpose, apparatuses for incinerating the combustible radioactive waste are widely established recently.
In such kind of apparatus for incinerating the combustible radioactive waste, it is important to completely incinerate the radioactive waste and remove the radioactive dust from the waste gas. In order to effect after burning of unincinerated components contained in the waste gas and at the same time remove the radioactive dust contained in the waste gas, a ceramic filter is widely used.
The ceramic filter has advantages that it can be used at a high temperature of the waste gas delivered from an incinerator, and that it can not only remove the radioactive dust but also effect after burning of the unincinerated components which have not sufficiently been incinerated in the incinerator. As a result, the ceramic filter is significantly usable in an apparatus for treating the waste gas delivered from the incinerator for incinerating radioactive waste.
The ceramic filter, however, has disadvantages that a ceramic filter element becomes clogged with the radioactive matter or so degraded in its mechanical strength that it is fallen down from its support plate after a longtime use. In order to avoid such disadvantages, it is necessary to exchange a spent filter element for a new one and also treat the spent filter element. In this case, the radioactive dust is deposited on the outer surface of the spent filter element and in addition the inside wall of a filter chamber is contaminated with the radioactive dust so that the spent filter element must also be treated as the radioactive waste. In exchanging the spent filter element for the new one, there exists such counter-measure that the operator is not subjected to such internal exposure as he absorbs the radioactive dust and that the radioactive contamination caused by scattering of the radioactive dust does not occur. In addition, the operator is required to exchange the spent filter element for the new one in a short time without approaching too near the spent filter element for fear that the operator should be subjected to unnecessary external exposure.
Heretofore, it has been the common practice to evacuate the filter chamber from its lower part so as to make slightly vacuum therein or maintain a reduced pressure which is slightly lower than the atmospheric pressure therein, thereby preventing the radioactive dust from being scattered from the filter chamber toward the upper part thereof, and exchange the spent filter element for the new one by an operator who wears a dust mask. Such measure, however, has disadvantages that in any case it is not possible to avoid scattering of a minute amount of radioactive dust into the operating house and hence the radioactive contamination is liable to be occurred, and that the exchange of the spent filter element for the new one becomes troublesome in operation since the operator must wear the dust mask.
A method of exchanging the spent filter element for the new one with the aid of the filter chamber which is provided at its upper part with a glove box has also been proposed. This method is capable of suppressing the scattering of the radioactive dust, but has disadvantages that it is troublesome in operation and requires a relatively long operating time, and that the operator must approach too near the radioactive matter to disregard the external exposure dose.
As a method of treating the spent filter element, heretofore, it has been the common practice to pulverize the spent filter element by means of a hammer in a glove box mounted at the lower part of the filter chamber, enclose the spent filter element thus pulverized in a storage container mounted at the lower part of the glove box and then solidify it with the aid of a cement, and finally store in a storage house.
This method, however, has disadvantages that the spent ceramic filter element is required to be pulverized by a human power, that the use of the glove box makes the operation difficult and requires a labor for a long time, that there is a risk of the operator being subjected to the external exposure by his position near the radioactive matter, that it is difficult to finely pulverize the ceramic filter element so that use must be made of a coarse ceramic which could not be densely enclosed in a storage container, and that such coarse ceramic not only could not sufficiently reduce its volume but also is difficult to sufficiently mix with cement when it is solidified.
In FIG. 6 is shown a typical waste gas treating installation which makes use of the above mentioned ceramic filter device and is capable of purifying waste gas containing radioactive matter. The installation shown in FIG. 6 is composed of a filter chamber 1 which is provided at its inner upper part with a support plate 2 from which are suspended downwardly a number of filter elements 3.
In FIG. 7 is shown one of these ceramic filter elements 3 downwardly suspended from the support plate 2. As shown in FIG. 7, the ceramic filter element 3 is provided at its top end with a flange 4 and an asbestos layer 5 sandwiched between the flange 4 and the support plate 2 in a sealed manner. The waste gas containing radioactive matter and delivered from an incinerator (not shown) is introduced through an inlet 6 into the filter chamber 1 and filtered by the ceramic filter elements 3. Unincinerated components contained in the waste gas are adhered to the surface of the ceramic filter elements 3 and then subjected to after burning at a temperature of 500.degree. C to 1,000.degree. C on the surface of the filter chamber 1. Both the filtration and after burning cause the waste gas to be purified and made harmless. The pure and harmlss gas thus treated is exhausted from an outlet 7.
Such prior art waste gas treating installation, however, has disadvantages that the use of asbestos for sealing a gap formed between the support plate 2 on the one hand and the ceramic filter element 3 and its upper flange 4 on the other hand requires a long time for exchanging the spent ceramic filter element 3 for the new one, that it is difficult to mechanize such exchange operation, and that if the asbestos is not uniformly compacted into the gap, the radioactive dust is liable to be leaked into the outlet 7, thereby producing dangerous radioactive contamination.